Computer not POSTing (sort of)

[Katar]

Okay my brother has been having a lot of problems with turning his computer on. He had problems before and got a replacement MB and then a replacement CPU from the retailer. He had to update his the Motherboard BIOS to get it to accept the new chip.

All was fine for a few weeks, when it stopped turning on immediately. It powers up all the fans like it is going to turn on, then they all power down again, then they power up again, it continues to do that for anywhere up to 3-4 hours then the machine starts and works perfectly (when it was starting properly before the fault the fans never made so much noise as they do when they are cycling like this). During the fans cycling power up/down nothing shows on the monitor and it nevers gets to either the GPU or MB BIOS screens. He sent the CPU and MB back again and they couldn't find anything wrong with either of them it boots up perfectly when they try it.

So we concluded it must be something else. Now we've tried 3 PSUs, 2 GPUs to try and fix the problem none helped. I can't remember if we changed the memory for this problem or for the original faultly MB, but I'm not going to take apart my perfectly workly PC for the memory (we don't have any spare), but wouldn't the motherboard get to BIOS even without memory? The only other thing that has remained constant throughout our testing that wasn't returned to the retailer for testing was the CPU cooler, could that be causing the problem? We have also unplugged everthing and plugged it all back in again several times.

Can't remember the name of the MB and CPU exactly but off the top of head they are a Gigabyte AMD 790FX and an AMD 9550 Phenom. Any help would be appreciated.

[peterb]

Test the memory using memtest 86+ (Google for it, download it and burn to CD, then boot off the CD if the machine will let you.

Check the CPU is properly seated on the CPU to eliminate\ overheating as a cause. What rating were the replacement PSUs?

[Katar]

Okay we tried a 700W, a 650W and 480W PSUs. My Pc is running perfectly fine off a 520W PSU and the only difference between the two machines is mine is an Intel CPU.

We have now tried putting in an old (and potentially faulty, it's the only spare AMD chip of the correct size) CPU into the MB and the same problem occurs. Trying the MB without any memory plugged has no effect on the problem, same for no CPU cooler attached. No CPU in the MB and the fans spin continously at 100%. Memory testing hasn't shown up any problems.

The only thing I can think of doing now is digging out the AMD supplied cooler and trying it rather then the after market model we are using atm.

[Bluecube]

Eliminating the blindingly obvious - have you tried plugging the PC into a different wall socket?

Providing that the supplier really did test the mobo and CPU then it seems you've done everything correctly (replacing GPU/ CPU/ PSU/ etc)

[Katar]

Well we've tried everything I can think of now. There must be a problem with either the MB or the power button on the case, the only two things connected on every test.

He's just going to chuck the MB and get an Intel chip and board. We've had no end of trouble trying to get refunds on faulty MBs from the retailer before, anything else they've managed to test and replace promptly but a MB we have to send back on average 3 times (and pay for postage and testing) before they identify a fault . He's also had crappy luck with AMD chips as well.

[Katar]

Heh. Next time I help out someone with a problem I am going to treat them like a complete idiot.

It turns out his removing the memory to test it wasn't quite as thorough as it should of been (I couldn't be bothered to watch him do all the testing). In his defence both sticks in his machine seem to have developed the same fault, but a quick test with some stuff from my machine and all works great, wasted a couple of hundred on a new MB and CPU but I think he has learnt his lession .